Xp is simply a rsource pig, it doesn't take much for it to start crawling.
I am forced to use an X Pro box for one client's network and it's a constant pain in the butt, compared to my Linux, Win98 and Win2K boxes.
This site has some cool registry tips ad various tweaks to get the basic OS running more efficiently.
http://www.tweakxp.com/
I have found most of the regedits to be straight forward (most are common for Windows) and none have given me any problems, but you should ALWAYS make a backp copy of yhe registry before editing.
When in the registry editor, just go to FILE>EXPORT and it will export a copy for recovery if needed.
I haven't installed SP2 yet as it was originally quite buggy and new things popup daily it seems.
I fid the best rule of thumg, unless you are havig dire issues that a SP will resolve, WAIT ON THEM!! usually a week or two minimum will allow any bugs to be found by those who just jump on patches so by the time you go to install it, there are already new updates available to resole any issues.